V.M. Darras (Veerle)http://repub.eur.nl/ppl/6372/
List of Publicationsenhttp://repub.eur.nl/eur_signature.pnghttp://repub.eur.nl/
RePub, Erasmus University RepositoryKnockdown of type 3 iodothyronine deiodinase severely perturbs both embryonic and early larval development in zebrafishhttp://repub.eur.nl/pub/63396/
Tue, 01 Apr 2014 00:00:01 GMT<div>M. Heijlen</div><div>A.M. Houbrechts</div><div>H. Bagci</div><div>S.L.J. van Herck</div><div>S. Kersseboom</div><div>C.V. Esguerra</div><div>R. Blust</div><div>T.J. Visser</div><div>D. Knapen</div><div>V.M. Darras</div>
Exposure to appropriate levels of thyroid hormones (THs) at the right time is of key importance for normal development in all vertebrates. Type 3 iodothyronine deiodinase (D3) is the prime TH-inactivating enzyme, and its expression is highest in the early stages of vertebrate development, implying that it may be necessary to shield developing tissues from overexposure to THs. We used antisense morpholino knockdown to examine the role of D3 during early development in zebrafish. Zebrafish possess 2 D3 genes, dio3a and dio3b. Here, we show that both genes are expressed during development and both contribute to in vivo D3 activity. However, dio3b mRNA levels inembryosare higher, and the effects of dio3b knockdownonD3activityandonthe resulting phenotype are more severe. D3 knockdown induced an overall delay in development, as determined by measurements of otic vesicle length, eye and ear size, and body length. The time of hatching was also severely delayed in D3-knockdown embryos. Importantly, we also observed a severe disturbance of several aspects of development. Swim bladder development and inflation was aberrant as was the development of liver and intestine. Furthermore, D3-knockdown larvae spent significantly less time moving, and both embryos and larvae exhibited perturbed escape responses, suggesting that D3 knockdown affects muscle development and/or functioning. These data indicate that D3 is essential for normal zebrafish embryonic and early larval development and show the value of morpholino knockdown in this model to further elucidate the specific role of D3 in some aspects of vertebrate development. CopyrightTransporters MCT8 and OATP1C1 maintain murine brain thyroid hormone homeostasishttp://repub.eur.nl/pub/54532/
Wed, 01 Jan 2014 00:00:01 GMT<div>S. Mayerl</div><div>J. Müller</div><div>R. Bauer</div><div>S. Richert</div><div>C.M. Kassmann</div><div>V.M. Darras</div><div>K. Buder</div><div>A. Boelen</div><div>T.J. Visser</div><div>H. Heuer</div>
Tissue-specific alterations in thyroid hormone homeostasis in combined Mct10 and Mct8 deficiencyhttp://repub.eur.nl/pub/63994/
Wed, 01 Jan 2014 00:00:01 GMT<div>J. Müller</div><div>S. Mayerl</div><div>T.J. Visser</div><div>V.M. Darras</div><div>A. Boelen</div><div>L. Frappart</div><div>L. Mariotta</div><div>F. Verrey</div><div>H. Heuer</div>
The monocarboxylate transporter Mct10 (Slc16a10; T-type amino acid transporter) facilitates the cellular transport of thyroid hormone (TH) and shows an overlapping expression with the wellestablished TH transporter Mct8. Because Mct8 deficiency is associated with distinct tissue-specific alterations in TH transport and metabolism, we speculated that Mct10 inactivation may compromise the tissue-specific TH homeostasis as well. However, analysis of Mct10 knockout (ko) mice revealed normal serum TH levels and tissue TH content in contrast to Mct8 ko mice that are characterized by high serum T3, low serum T4, decreased brain TH content, and increased tissue TH concentrations in the liver, kidneys, and thyroid gland. Surprisingly, mice deficient in both TH transporters (Mct10/Mct8 double knockout [dko] mice) showed normal serum T4 levels in the presence of elevated serum T 3, indicating that the additional inactivation of Mct10 partially rescues the phenotype of Mct8 ko mice. As a consequence of the normal serum T4, brain T4 content and hypothalamic TRH expression were found to be normalized in the Mct10/Mct8 dko mice. In contrast, the hyperthyroid situation in liver, kidneys, and thyroid gland of Mct8 ko mice was even more severe in Mct10/Mct8 dko animals, suggesting that in these organs, both transporters contribute to the TH efflux. In summary, our data indicate that Mct10 indeed participates in tissue-specific TH transport and also contributes to the generation of the unusual serum TH profile characteristic for Mct8 deficiency. CopyrightMonocarboxylate Transporter 8 Modulates the Viability and Invasive Capacity of Human Placental Cells and Fetoplacental Growth in Micehttp://repub.eur.nl/pub/70127/
Wed, 12 Jun 2013 00:00:01 GMT<div>E. Vasilopoulou</div><div>L.S. Loubière</div><div>H. Heuer</div><div>M. Trajkovic-Arsic</div><div>V.M. Darras</div><div>T.J. Visser</div><div>G.E. Lash</div><div>R.D. Whitley</div><div>M. McCabe</div><div>J.A. Franklyn</div><div>M.D. Kilby</div><div>S.-Y. Chan</div>
Monocarboxylate transporter 8 (MCT8) is a well-established thyroid hormone (TH) transporter. In humans, MCT8 mutations result in changes in circulating TH concentrations and X-linked severe global neurodevelopmental delay. MCT8 is expressed in the human placenta throughout gestation, with increased expression in trophoblast cells from growth-restricted pregnancies. We postulate that MCT8 plays an important role in placental development and transplacental TH transport. We investigated the effect of altering MCT8 expression in human trophoblast in vitro and in a Mct8 knockout mouse model. Silencing of endogenous MCT8 reduced T3 uptake into human extravillous trophoblast-like cells (SGHPL-4; 40%, P<0.05) and primary cytotrophoblast (15%, P<0.05). MCT8 over-expression transiently increased T3 uptake (SGHPL-4:30%, P<0.05; cytotrophoblast: 15%, P<0.05). Silencing MCT8 did not significantly affect SGHPL-4 invasion, but with MCT8 over-expression T3 treatment promoted invasion compared with no T3 (3.3-fold; P<0.05). Furthermore, MCT8 silencing increased cytotrophoblast viability (∼20%, P<0.05) and MCT8 over-expression reduced cytotrophoblast viability independently of T3 (∼20%, P<0.05). In vivo, Mct8 knockout reduced fetal:placental weight ratios compared with wild-type controls at gestational day 18 (25%, P<0.05) but absolute fetal and placental weights were not significantly different. The volume fraction of the labyrinthine zone of the placenta, which facilitates maternal-fetal exchange, was reduced in Mct8 knockout placentae (10%, P<0.05). However, there was no effect on mouse placental cell proliferation in vivo. We conclude that MCT8 makes a significant contribution to T3 uptake into human trophoblast cells and has a role in modulating human trophoblast cell invasion and viability. In mice, Mct8 knockout has subtle effects upon fetoplacental growth and does not significantly affect placental cell viability probably due to compensatory mechanisms in vivo.Hypothyroidism compromises hypothalamic leptin signaling in micehttp://repub.eur.nl/pub/60655/
Mon, 01 Apr 2013 00:00:01 GMT<div>C. Groba</div><div>S. Mayerl</div><div>A.A.A. van Mullem</div><div>T.J. Visser</div><div>V.M. Darras</div><div>A.J. Habenicht</div><div>H. Heuer</div>
The impact of thyroid hormone (TH) on metabolism and energy expenditure is well established, but the role of TH in regulating nutritional sensing, particularly in the central nervous system, is only poorly defined. Here, we studied the consequences of hypothyroidism on leptin production as well as leptin sensing in congenital hypothyroid TRH receptor 1 knockout (Trhr1 ko) mice and euthyroid control animals. Hypothyroid mice exhibited decreased circulating leptin levels due to a decrease in fat mass and reduced leptin expression in white adipose tissue. In neurons of the hypothalamic arcuate nucleus, hypothyroid mice showed increased leptin receptor Ob-R expression and decreased suppressor of cytokine signaling 3 transcript levels. In order to monitor putative changes in central leptin sensing, we generated hypothyroid and leptin-deficient animals by crossing hypothyroid Trhr1 ko mice with the leptin-deficient ob/ob mice. Hypothyroid Trhr1/ob double knockout mice showed a blunted response to leptin treatment with respect to body weight and food intake and exhibited a decreased activation of phospho-signal transducer and activator of transcription 3 as well as a up-regulation of suppressor of cytokine signaling 3 upon leptin treatment, particularly in the arcuate nucleus. These data indicate alterations in the intracellular processing of the leptin signal under hypothyroid conditions and thereby unravel a novel mode of action by which TH affects energy metabolism.Impact of Oatp1c1 deficiency on thyroid hormone metabolism and action in the mouse brainhttp://repub.eur.nl/pub/64057/
Thu, 01 Mar 2012 00:00:01 GMT<div>S. Mayerl</div><div>T.J. Visser</div><div>V.M. Darras</div><div>S. Horn</div><div>H. Heuer</div>
Organic anion-transporting polypeptide 1c1 (Oatp1c1) (also known as Slco1c1 and Oatp14) belongs to the family of Oatp and has been shown to facilitate the transport of T 4. In the rodent brain, Oatp1c1 is highly enriched in capillary endothelial cells and choroid plexus structures where it may mediate the entry of T 4 into the central nervous system. Here, we describe the generation and first analysis of Oatp1c1-deficient mice. Oatp1c1 knockout (KO) mice were born with the expected frequency, were not growth retarded, and developed without any overt neurological abnormalities. Serum T 3 and T 4 concentrations as well as renalandhepatic deiodinase type 1 expression levels were indistinguishable between Oatp1c1 KO mice and control animals. Hypothalamic TRH and pituitaryTSH mRNA levels were not affected, but brain T 4 and T 3 content was decreased in Oatp1c1-deficient animals. Moreover, increased type 2 and decreased type 3 deiodinase activities indicate a mild hypothyroid situation in the brain of Oatp1c1 KO mice. Consequently, mRNA expression levels of gene products positively regulated by T 3 in the brain were down-regulated. This central nervous system-specific hypothyroidism is presumably caused by an impaired passage of T 4 across the blood-brain barrier and indicates a unique function of Oatp1c1 in facilitating T 4 transport despite the presence of other thyroid hormone transporters such as Mct8. CopyrightImpact of monocarboxylate transporter-8 deficiency on the hypothalamus-pituitary-thyroid axis in micehttp://repub.eur.nl/pub/27557/
Fri, 01 Oct 2010 00:00:01 GMT<div>M. Trajkovic-Arsic</div><div>J. Müller</div><div>V.M. Darras</div><div>C. Groba</div><div>S. Lee</div><div>D. Weih</div><div>K. Bauer</div><div>T.J. Visser</div><div>H. Heuer</div>
In patients, inactivating mutations in the gene encoding the thyroid hormone-transporting monocarboxylate transporter 8 (Mct8) are associated with severe mental and neurological deficits and disturbed thyroid hormone levels. The latter phenotype characterized by high T3and low T4serum concentrations is replicated in Mct8 knockout (ko) mice, indicating that MCT8 deficiency interferes with thyroid hormone production and/or metabolism. Our studies of Mct8 ko mice indeed revealed increased thyroidal T3and T4concentrations without overt signs of a hyperactive thyroid gland. However, upon TSH stimulation Mct8 ko mice showed decreased T4and increased T3secretion compared with wild-type littermates. Moreover, similar changes in the thyroid hormone secretion pattern were observed in Mct8/Trhr1 double-ko mice, which are characterized by normal serum T3levels and normal hepatic and renal D1 expression in the presence of very low T4serum concentrations. These data strongly indicate that absence of Mct8 in the thyroid gland affects thyroid hormone efflux by shifting the ratio of the secreted hormones toward T3. To test this hypothesis, we generated Mct8/Pax8 double-mutant mice, which in addition to Mct8 lack a functional thyroid gland and are therefore completely athyroid. Following the injection of these animals with either T4or T3, serum analysis revealed T3concentrations similar to those observed in Pax8 ko mice under thyroid hormone replacement, indicating that indeed increased thyroidal T3secretion in Mct8 ko mice represents an important pathogenic mechanism leading to the high serum T3levels. Copyright Consequences of monocarboxylate transporter 8 deficiency for renal transport and metabolism of thyroid hormones in micehttp://repub.eur.nl/pub/27515/
Fri, 29 Jan 2010 00:00:01 GMT<div>M. Trajkovic-Arsic</div><div>T.J. Visser</div><div>V.M. Darras</div><div>E.C.H. Friesema</div><div>B. Schlott</div><div>J. Mittag</div><div>K. Bauer</div><div>H. Heuer</div>
Patients carrying inactivating mutations in the gene encoding the thyroid hormone transporting monocarboxylate transporter (MCT)-8 suffer from a severe form of psychomotor retardation and exhibit abnormal serum thyroid hormone levels. The thyroidal phenotype characterized by highserum T3and low-serum T4levels is also found in mice mutants deficient in MCT8 although the cause of these abnormalities is still unknown. Here we describe the consequences of MCT8 deficiency for renal thyroid hormone transport, metabolism, and function by studying MCT8 null mice and wild-type littermates. Whereas serum and urinary parameters do not indicate a strongly altered renal function, a pronounced induction of iodothyronine deiodinase type 1 expression together with increased renal T3and T4content point to a general hyperthyroid state of the kidneys in the absence of MCT8. Surprisingly, accumulation of peripherally injected T4and T3into the kidneys was found to be enhanced in the absence of MCT8, indicating that MCT8 deficiency either directly interferes with the renal efflux of thyroid hormones or activates indirectly other renal thyroid hormone transporters that preferentially mediate the renal uptake of thyroid hormones. Our findings indicate that the enhanced uptake and accumulation of T4in the kidneys of MCT8 null mice together with the increased renal conversion of T4into T3by increased renal deiodinase type 1 activities contributes to the generation of the low-serum T4and the increase in circulating T3levels, a hallmark of MCT8 deficiency. Copyright Expression of thyroid hormone transporters during critical illnesshttp://repub.eur.nl/pub/25400/
Fri, 27 Nov 2009 00:00:01 GMT<div>L. Mebis</div><div>D. Paletta</div><div>Y. Debaveye</div><div>B. Ellger</div><div>L. Langouche</div><div>A. D'Hoore</div><div>V.M. Darras</div><div>T.J. Visser</div><div>G. van den Berghe</div>
Objective: Prolonged critically ill patients have low circulating thyroid hormone (TH) levels without a rise in TSH, a condition labeled 'the low tri-iodothyronine (T3) syndrome'. Currently, it is not clear whether this represents an adaptive response. We examined the role of TH transporters monocarboxylate transporter 8 (MCT8, also known as SLC16A2) and MCT10 in the pathogenesis of the low T3 syndrome in prolonged critical illness. Methods: A clinical observational study in critically ill patients and an intervention study in an in vivo animal model of critical illness. Gene expression levels of MCT8 and MCT10 were measured by realtime PCR. Results: In prolonged critically ill patients, we measured increased MCT8 but not MCT10 gene expression levels in liver and skeletal muscle as compared with patients undergoing acute surgical stress. In a rabbit model of prolonged critical illness, gene expression levels of MCT8 in liver and of MCT10 in skeletal muscle were increased as compared with healthy controls. Treatment of prolonged critically ill rabbits with TH (thyroxineCT3) resulted in a downregulation of gene expression levels of MCT8 in liver and of MCT10 in muscle. Transporter expression levels correlated inversely with circulating TH parameters. Conclusions: These data suggest that alterations in the expression of TH transporters do not play a major role in the pathogenesis of the 'low T3 syndrome' but rather reflect a compensatory effort in response to hypothyroidism. Changes in the central component of the hypothalamus-pituitary-thyroid axis in a rabbit model of prolonged critical illnesshttp://repub.eur.nl/pub/25355/
Fri, 11 Sep 2009 00:00:01 GMT<div>L. Mebis</div><div>Y. Debaveye</div><div>B. Ellger</div><div>S. Derde</div><div>E.J. Ververs</div><div>L. Langouche</div><div>V.M. Darras</div><div>E. Fliers</div><div>T.J. Visser</div><div>G. van den Berghe</div>
Introduction: Prolonged critically ill patients reveal low circulating thyroid hormone levels without a rise in thyroid stimulating hormone (TSH). This condition is labeled "low 3,5,3'-tri-iodothyronine (T3) syndrome" or "nonthyroidal illness syndrome (NTI)" or "euthyroid sick syndrome". Despite the low circulating and peripheral tissue thyroid hormone levels, thyrotropin releasing hormone (TRH) expression in the hypothalamus is reduced and it remains unclear which mechanism is responsible. We set out to study whether increased hypothalamic T3availability could reflect local thyrotoxicosis and explain feedback inhibition-induced suppression of the TRH gene in the context of the low T3syndrome in prolonged critical illness.Methods: Healthy rabbits were compared with prolonged critically ill, parenterally fed animals. We visualized TRH mRNA in the hypothalamus by in situ-hybridization and measured mRNA levels for the type II iodothyronine diodinase (D2), the thyroid hormone transporters monocarboxylate transporter (MCT) 8, MCT10 and organic anion co-transporting polypeptide 1C1 (OATP1C1) and the thyroid hormone receptors α (TRα) and β (TRβ) in the hypothalamus. We also measured the activity of the D2 and type III iodothyronine deiodinase (D3) enzymes.Results: In the hypothalamus of prolonged critically ill rabbits with low circulating T3 and TSH, we observed decreased TRH mRNA, increased D2 mRNA and increased MCT10 and OATP1C1 mRNA while MCT8 gene expression was unaltered as compared with healthy controls. This coincided with low hypothalamic thyroxine (T4) and low-normal T3concentrations, without a change at the thyroid hormone receptor level.Conclusions: Although expression of D2 and of the thyroid hormone transporters MCT10 and OATP1C1 were increased in the hypothalamus of prolonged critical ill animals, hypothalamic T4and T3content or thyroid hormone receptor expression were not elevated. Hence, decreased TRH gene expression, and hereby low TSH and T3 during prolonged critical illness, is not exclusively brought about by hypothalamic thyrotoxicosis, and infer other TRH suppressing factors to play a role. Large induction of type III deiodinase expression after partial hepatectomy in the regenerating mouse and rat liverhttp://repub.eur.nl/pub/25469/
Thu, 01 Jan 2009 00:00:01 GMT<div>M.H.A. Kester</div><div>M.J.M. Toussaint</div><div>C.A. Punt</div><div>R. Matondo</div><div>A.M. Aarnio</div><div>V.M. Darras</div><div>M.E. Everts</div><div>A. de Bruin</div><div>T.J. Visser</div>
The deiodinase types 1 (D1) and 2 (D2) catalyze the activation of T4to T3, whereas type 3 deiodinase (D3) catalyzes the inactivation of T3and T4. D3 plays a key role in controlling thyroid hormone bioavailability. It is highly expressed during fetal development, but also in other processes with increased cell proliferation, e.g. in vascular tumors. Because tissue regeneration is dependent on cellular proliferation and is associated with activation of fetal genes, we evaluated deiodinase activities and mRNA expression in rat and mouse liver, as well as the local and systemic thyroid hormone status after partial hepatectomy (PH). We observed that in rats, D3 activity was increased 10-fold at 20 h and 3-fold at 48 h after PH; D3 mRNA expression was increased 3-fold at 20 h. The increase in D3 expression was associated with maximum 2-to 3-fold decreases of serum and liver T3and T4levels at 20 to 24 h after PH. In mice, D3 activity was increased 5-fold at 12 h, 8-fold at 24 h, 40-fold at 36 h, 15-fold at 48 h, and 7-fold at 72 h after PH. In correlation with this, D3 mRNA was highest (6-fold increase), and serum T3and T4were lowest at 36 h. Furthermore, as a measure for cell proliferation, 5-bromo-2'- deoxyuridine incorporation peaked at 20-24 h after PH in rats and at 36 h in mice. No significant effect on D1 activity or mRNA expression was found after PH. D2 activity was always undetectable. In conclusion, we found a large induction of hepatic D3 expression after PH that was correlated with an increased cellular proliferation and decreased serum and liver T3and T4levels. Our data suggest that D3 is important in the modulation of thyroid hormone levels in the regenerating liver, in which a decrease in cellular T3permits an increase in proliferation. (Endocrinology 150: 540-545, 2009) Copyright Effects of substitution and high-dose thyroid hormone therapy on deiodination, sulfoconjugation, and tissue thyroid hormone levels in prolonged critically ill rabbitshttp://repub.eur.nl/pub/29017/
Fri, 01 Aug 2008 00:00:01 GMT<div>Y. Debaveye</div><div>B. Ellger</div><div>L. Mebis</div><div>T.J. Visser</div><div>V.M. Darras</div><div>G. van den Berghe</div>
To delineate the metabolic fate of thyroid hormone in prolonged critically ill rabbits, we investigated the impact of two dose regimes of thyroid hormone on plasma 3,3′-diiodothyronine (T2) and T4S, deiodinase type 1 (D1) and D3 activity, and tissue iodothyronine levels in liver and kidney, as compared with saline and TRH. D2-expressing tissues were ignored. The regimens comprised either substitution dose or a 3- to 5- fold higher dose of T4and T3, either alone or combined, targeted to achieve plasma thyroid hormone levels obtained by TRH. Compared with healthy animals, saline-treated ill rabbits revealed lower plasma T3(P = 0.006), hepatic T3(P = 0.02), and hepatic D1 activity (P = 0.01). Substitution-dosed thyroid hormone therapy did not affect these changes except a further decline in plasma (P = 0.0006) and tissue T4(P = 0.04). High-dosed thyroid hormone therapy elevated plasma and tissue iodothyronine levels and hepatic D1 activity, as did TRH. Changes in iodothyronine tissue levels mimicked changes in plasma. Tissue T3and tissue T3/reverse T3ratio correlated with deiodinase activities. Neither substitution- nor high-dose treatment altered plasma T2. Plasma T4S was increased only by T4in high dose. We conclude that in prolonged critically ill rabbits, low plasma T3levels were associated with low liver and kidney T3levels. Restoration of plasma and liver and kidney tissue iodothyronine levels was not achieved by thyroid hormone in substitution dose but instead required severalfold this dose. This indicates thyroid hormone hypermetabolism, which in this model of critical illness is not entirely explained by deiodination or by sulfoconjugation. Copyright Abnormal thyroid hormone metabolism in mice lacking the monocarboxylate transporter 8http://repub.eur.nl/pub/35563/
Thu, 01 Mar 2007 00:00:01 GMT<div>M. Trajkovic</div><div>T.J. Visser</div><div>J. Mittag</div><div>S. Horn</div><div>J. Lukas</div><div>V.M. Darras</div><div>G. Raivich</div><div>K. Bauer</div><div>H. Heuer</div>
In humans, inactivating mutations in the gene of the thyroid hormone transporter monocarboxylate transporter 8 (MCT8; SLC16A2) lead to severe forms of psychomotor retardation combined with imbalanced thyroid hormone serum levels. The MCT8-null mice described here, however, developed without overt deficits but also exhibited distorted 3,5,3′-triiodothyronine (T3) and thyroxine (T4) serum levels, resulting in increased hepatic activity of type 1 deiodinase (D1). In the mutants' brains, entry of T4 was not affected, but uptake of T3 was diminished. Moreover, the T4 and T3 content in the brain of MCT8-null mice was decreased, the activity of D2 was increased, and D3 activity was decreased, indicating the hypothyroid state of this tissue. In the CNS, analysis of T3 target genes revealed that in the mutants, the neuronal T3 uptake was impaired in an area-specific manner, with strongly elevated thyrotropin-releasing hormone transcript levels in the hypothalamic paraventricular nucleus and slightly decreased RC3 mRNA expression in striatal neurons; however, cerebellar Purkinje cells appeared unaffected, since they did not exhibit dendritic outgrowth defects and responded normally to T3 treatment in vitro. In conclusion, the circulating thyroid hormone levels of MCT8-null mice closely resemble those of humans with MCT8 mutations, yet in the mice, CNS development is only partially affected.Deiodinase activity is present in Xenopus laevis during early embryogenesishttp://repub.eur.nl/pub/61572/
Fri, 22 Sep 2006 00:00:01 GMT<div>G.M. Dubois</div><div>A. Sebillot</div><div>G.G.J.M. Kuiper</div><div>C.H.J. Verhoelst</div><div>V.M. Darras</div><div>T.J. Visser</div><div>B.A. Demeneix</div>
Thyroid hormones orchestrate amphibian metamorphosis. The type 2 and type 3 deiodinases make vital contributions to this process by controlling levels of the thyroid hormones T4 and T3 available to different tissues. Because the tadpole thyroid gland is not functional until stage NF44, it has been widely assumed that thyroid signaling is absent during amphibian early development, thyroid hormone only becoming a major regulator during premetamorphic stages. Similarly, in mammals, thyroid function is known to be essential to neuronal development, especially during the perinatal stages, but again little is known about early stages of development. Here we demonstrate that key elements of thyroid hormone signaling are present during early development of Xenopus. In particular, we find functional thyroid hormone-activating deiodinases and significant levels of their substrates, T4 and T3, during early embryogenesis. Furthermore, we have further characterized a recently identified deiodinase in amphibians, homologous to mammalian type 1 deiodinase (D1). This enzyme is expressed in marked, spatially defined patterns during embryogenesis. The patterns of expression of type 1 deiodinase are distinct from those of type 2 and type 3 deiodinases. Deiodinase expression is found in neurogenic areas from stage NF30 onward, both in the central and peripheral nervous systems. We conclude that both activating and inactivating deiodinases show dynamic patterns of expression during early embryogenesis in amphibians, particularly in neurogenic areas. These findings suggest that thyroid hormone signaling is a key component of early neuronal development in vertebrates. CopyrightCharacterization of recombinant Xenopus laevis type I iodothyronine deiodinase: Substitution of a proline residue in the catalytic center by serine (Pro132Ser) restores sensitivity to 6-propyl-2-thiouracilhttp://repub.eur.nl/pub/73549/
Fri, 23 Jun 2006 00:00:01 GMT<div>G.G.J.M. Kuiper</div><div>W. Klootwijk</div><div>G.M. Dubois</div><div>O. Destree</div><div>V.M. Darras</div><div>S. van der Geyten</div><div>B.A. Demeneix</div><div>T.J. Visser</div>
In frogs such as Rana and Xenopus, metamorphosis does not occur in the absence of a functional thyroid gland. Previous studies indicated that coordinated development in frogs requires tissue and stage-dependent type II and type III iodothyronine deiodinase expression patterns to obtain requisite levels of intracellular T3 in tissues at the appropriate stages of metamorphosis. No type I iodothyronine deiodinase (D1), defined as T4 or reverse T3 (rT3) outer-ring deiodinase (ORD) activity with Michaelis constant (Km) values in the micromolar range and sensitivity to 6-propyl-2-thiouracil (6-PTU), could be detected in tadpoles so far. We obtained a X. laevis D1 cDNA clone from brain tissue. The complete sequence of this clone (1.1 kb, including poly A tail) encodes an ORF of 252 amino acid residues with high homology to other vertebrate D1 enzymes. The core catalytic center includes a UGA-encoded selenocysteine residue, and the 3′ untranslated region (about 300 nt) contains a selenocysteine insertion sequence element. Transfection of cells with an expression vector containing the full-length cDNA resulted in generation of significant deiodinase activity in the homogenates. The enzyme displayed ORD activity with T4 (K m 0.5 μM) and rT3 (Km 0.5 μM) and inner-ring deiodinase activity with T4 (Km 0.4 μM). Recombinant Xenopus D1 was essentially insensitive to inhibition by 6-PTU (IC50 > 1 mM) but was sensitive to gold thioglucose (IC50 0.1 μM) and iodoacetate (IC50 10 μM). Because the residue 2 positions downstream from the selenocysteine is Pro in Xenopus D1 but Ser in all cloned PTU-sensitive D1 enzymes, we prepared the Pro132Ser mutant of Xenopus D1. The mutant enzyme showed strongly increased ORD activity with T4 and rT3 (Km about 4 μM) and was highly sensitive to 6-PTU (IC50 2 μM). Little native D1 activity could be detected in Xenopus liver, kidney, brain, and gut, but significant D1 mRNA expression was observed in juvenile brain and adult liver and kidney. These results indicate the existence of a 6-PTU-insensitive D1 enzyme in X. laevis tissues, but its role during tadpole metamorphosis remains to be defined. CopyrightDiagnostic challenges for Pompe disease: An under-recognized cause of floppy baby syndromehttp://repub.eur.nl/pub/69549/
Mon, 01 May 2006 00:00:01 GMT<div>R.R. Howell</div><div>B. Byrne</div><div>V.M. Darras</div><div>P. Kishnani</div><div>M. Nicolino</div><div>A.T. van der Ploeg</div>
Pompe disease, a disorder caused by a deficiency in the lysosomal enzyme acid alpha glucosidase, is frequently overlooked as a cause of floppy baby syndrome. The accurate diagnosis of floppy baby syndrome requires the sequential evaluation of medical causes (e.g., hypothyroidism, sepsis, malnutrition, malabsorption, congenital heart disease), neurologic etiologies (central [cerebral] and peripheral [lower motor unit]) and anatomic characteristics of the abnormality. Cardiomegaly on chest x-ray in a patient with floppy baby syndrome should alert the pediatrician to suspect Pompe disease. Based on this finding, further work-up or referral to a specialist can be considered. Pompe disease requires immediate attention. Symptomatic intervention of this disorder should be initiated at the earliest time possible to maximize the potential benefit from therapy and to prevent irreversible organ damage. Moreover, early diagnosis is important for providing parents with realistic information about their child's prognosis, and where appropriate, professional genetic counseling. Enzyme replacement therapy (ERT) with recombinant human GAA is currently being evaluated in clinical trials; the future availability of this option makes early identification of this condition even more critical. This article presents a unified view on the optimal approach to the accurate diagnosis of Pompe disease and to its recognition as one of the possible and treatable causes of floppy baby syndrome. CopyrightTissue thyroid hormone levels in critical illnesshttp://repub.eur.nl/pub/64502/
Thu, 01 Dec 2005 00:00:01 GMT<div>R.P. Peeters</div><div>S.D. van Geyten</div><div>P.J. Wouters</div><div>V.M. Darras</div><div>H. van Toor</div><div>E. Kaptein</div><div>T.J. Visser</div><div>G. van den Berghe</div>
Context: Pronounced alterations in serum thyroid hormone levels occur during critical illness. T3 decreases and rT3 increases, the magnitudes of which are related to the severity of disease. It is unclear whether these changes are associated with decreased tissue T3 concentrations and, thus, reduced thyroid hormone bioactivity. Patients and Study Questions: We therefore investigated, in 79 patients who died after intensive care and who did or did not receive thyroid hormone treatment, whether total serum thyroid hormone levels correspond to tissue levels in liver and muscle. Furthermore, we investigated the relationship between tissue thyroid hormone levels, deiodinase activities, and monocarboxylate transporter 8 expression. Results: Tissue iodothyronine levels were positively correlated with serum levels, indicating that the decrease in serum T3 during illness is associated with decreased levels of tissue T3. Higher serum T3 levels in patients who received thyroid hormone treatment were accompanied by higher levels of liver and muscle T3, with evidence for tissue-specific regulation. Tissue rT3 and the T 3/rT3 ratio were correlated with tissue deiodinase activities. Monocarboxylate transporter 8 expression was not related to the ratio of the serum over tissue concentration of the different iodothyronines. Conclusion: Our results suggest that, in addition to changes in the hypothalamus-pituitary-thyroid axis, tissue-specific mechanisms are involved in the reduced supply of bioactive thyroid hormone in critical illness. CopyrightHypothyroidism induces type I iodothyronine deiodinase expression in tilapia liverhttp://repub.eur.nl/pub/61148/
Sat, 01 Dec 2001 00:00:01 GMT<div>S. van der Geyten</div><div>A. Toguyeni</div><div>J.-F. Baroiller</div><div>B. Fauconneau</div><div>A. Fostier</div><div>J.P. Sanders</div><div>T.J. Visser</div><div>E.R. Kühn</div><div>V.M. Darras</div>
In the current study, the authors examined the effects of experimentally induced hypothyroidism on peripheral thyroid hormone metabolism and growth in two closely related tilapia species: the Nile tilapia (Oreochromis niloticus) and the slower growing black tilapia (Sarotherodon melanotheron). Hypothyroidism, induced by administration of 0.2% methimazole through the food, significantly decreased plasma T3 and T4 in both species. This decrease in circulating thyroid hormones was accompanied by an increase in hepatic type II deiodinase (D2) and a decrease in hepatic type III deiodinase (D3). Hepatic type I deiodinase (D1), which is barely expressed in euthyroid tilapia, was significantly upregulated during hypothyroidism. The changes in hepatic D1 and D2 enzyme activity were paralleled by changes in D1 and D2 mRNA levels, indicating pretranslational regulation. Hypothyroidism also resulted in severe growth retardation that was accompanied by an increase in condition factor. Because hyperthyroidism has been shown to decrease the condition factor, these results suggest that thyroid hormones play an essential role in the control of proportional body growth in fish. The authors conclude that (1) hepatic D1 expression is induced by hypothyroidism in tilapia, (2) the changes in hepatic iodothyronine deiodinases during hypothyroidism in tilapia are predominantly regulated at a pretranslational level, and (3) thyroid hormones are involved in the control of proportional body growth in fish.Regulation of thyroid hormone metabolism during fasting and refeeding in chickenhttp://repub.eur.nl/pub/62740/
Mon, 01 Nov 1999 00:00:01 GMT<div>S. van der Geyten</div><div>E. van Rompaey</div><div>J.P. Sanders</div><div>T.J. Visser</div><div>E.R. Kühn</div><div>V.M. Darras</div>
Regulation of thyroid hormone metabolism during fetal developmenthttp://repub.eur.nl/pub/74044/
Tue, 25 May 1999 00:00:01 GMT<div>V.M. Darras</div><div>R. Hume</div><div>T.J. Visser</div>